Abstract
Hydroxypropyl cellulose (HPC)/silica micro-hybrids with various amounts of nanometer-size silica particles were produced with a sol-gel process, by incorporating HPC with tetraethoxysilane-derived silica. The sorption isotherms of sol-gel-derived silica, HPC, and the HPC/silica micro-hybrids were measured at 30°C. The sol-gel-derived silica was porous and exhibited a 30% water regain (i.e., percent weight increase due to the absorbed water) at 100% relative humidity (RH). The HPC exhibited a sorption isotherm typical of hydrophilic polymers. Water sorption behavior of the HPC/silica micro-hybrids was almost the same as that of HPC. The dynamic viscoelastic properties of HPC and the HPC/silica micro-hybrids were measured as a function of RH at 30°C. The dynamic modulus, G′, of HPC decreased from 600 Mpa at 0% RH to 8 MPa at 80~100% RH, and the peak in the tan δ curve appeared at about 75% RH. This peak was caused by the onset of micro-Brownian motion by the sorbed water. For the HPC/silica micro-hybrids, G′ decreased only slightly as RH increased. This slight decrease may be caused by the strong interaction between the dispersed small silica particles and the HPC matrix, which prevents water-induced softening of the hybrids. In contrast to the HPC/silica micro-hybrids, the HPC composite blended with 20 wt% of unmodified glass beads exhibited the same viscoelastic behavior as HPC, due to the weak interaction between the glass beads and the HPC matrix.
